Sanitary napkins are well known in the art. Sanitary napkins intercept menses upon discharge, and thereby protect the clothing and bedding of the wearer from soiling by the menses.
However, sanitary napkins can and do bunch and rope during use. This occurrence reduces the target area of the sanitary napkin, allowing discharged menses to soil the undergarment of the wearer and causing wearer discomfort.
One attempt to deal with this problem is to provide the sanitary napkin with a means for resisting deformation under the action of the wearer's body movements. Such resistance to deformation is accomplished by providing a sanitary napkin having crush resistance. Crush resistance is related to the ability of the napkin to resist crushing forces applied to the longitudinal side edges of the napkin during use, in order to reduce unintended bending, twisting, and folding of the napkin. By making the sanitary napkin crush resistant, allegedly the sanitary napkin does not bunch or rope during use. A sanitary napkin alleging to have such crush resistance is taught in Bradstreet et al. U.S. Pat. No. 4,217,901 issued Aug. 19, 1980.
An improvement to this approach is to provide a sanitary napkin having both high flexibility and high capacity. Preferably such a sanitary napkin is thin, and closely conforms to the anatomy of the wearer. A thin, high flexibility, high capacity sanitary napkin provides the best of all worlds. A relatively thin napkin has less in use wearer awareness. A high flexibility napkin provides greater wearer comfort, without being obtrusive under tight clothing. A high capacity napkin can be worn during all days of the menstrual cycle.
Such a high flexibility, high capacity sanitary napkin conforms to and moves with the wearer, rather than resisting the actions and forces imposed by the wearer as taught by the aforementioned Bradstreet et al. U.S. Pat. No. 4,217,901. This arrangement provides the advantage of greater wearer comfort without an unintentional reduction in the target area. Such a sanitary napkin has met with great commercial success in recent years, and is made according to commonly assigned Osborn, III U.S. Pat. No. 4,950,264 issued Aug. 21, 1990 and commonly assigned Osborn, III U.S. Pat. No. 5,009,653 issued Apr. 23, 1991. The foregoing U.S. Pat. Nos. 4,950,264 and 5,009,653 are incorporated herein by reference.
However, there remains a need for a thin, high flexibility, high capacity sanitary napkin which is even less crush resistant than those made according to U.S. Pat. Nos. 4,950,264 and 5,009,653. Such a sanitary napkin must not provide unintended or uncomfortable resistance to lateral compression from the thighs of the wearer, and yet still conform to the anatomy of the wearer. One manner in which this may be accomplished is by longitudinally weakening the sanitary napkin so that a line of weakness, such as a hinge line, results.
One such attempt in the art provides a longitudinally articulated sanitary napkin as found in Chesky et al. U.S. Pat. No. 3,954,107 issued May 4, 1976. However, the Chesky et al. sanitary napkin does not have a generally planar topsheet. The topsheet is interrupted by a channel having the shape of an inverted T. This arrangement requires the sanitary napkin to have more thickness than is necessary, and thereby provides an unduly high degree of wearer awareness.
Other attempts have been made in the art to provide longitudinal grooves in a sanitary napkin. For example, Luceri et al. U.S. Pat. No. 4,795,455 issued Jan. 3, 1989 discloses a napkin pad liner having a longitudinal channel embossed along nearly the entire length of the liner. This arrangement provides a high density region in the center, allegedly improving longitudinal fluid distribution. However, this arrangement has the drawback that fluid may not properly laterally wick into the storage areas laterally outboard of the channel.
Other embodiments of Luceri et al. show opposed channels, one on either face of the napkin pad liner. This arrangement provides the disadvantage that the sanitary napkin is predisposed to bend either concave up or concave down, causing a less predictable performance.
In a similar attempt, Richards U.S. Pat. No. 4,059,114 issued Nov. 22, 1977 discloses an absorbent pad having embossments in the web. This arrangement again, has the embossments in the top surface of the napkin and relies upon the fluid handling characteristics noted above. Moreover, a channel embossed in the top of the sanitary napkin predisposes it to bend in a concave upward configuration, rather than a preferred convex upward configuration. A similar attempt is found in Romans-Hess et al. U.S. Pat. No. 4,655,759 issued Apr. 7, 1987 which discloses a sanitary napkin having embossed channels adjacent the longitudinal side edges to minimize side staining to eliminate leakage and allow the sides of the napkin to fold upwards during use.
Yet other attempts in the art to provide longitudinal lines of weakness in the top surface of the sanitary napkin include Glassman U.S. Pat. No. 3,343,543 issued Sep. 26, 1967; Mogor U.S. Pat. No. 3,575,174 issued Apr. 20, 1971; and Kamstrup-Larsen U.S. Pat. No. 4,840,692 issued Jun. 20, 1989. However, these arrangements all disclose multiple lines of weakness and/or relatively thick napkins. Multiple lines of weakness may not require the sanitary napkin to buckle along the center. Relatively thick napkins suffer from the disadvantages noted above.
Yet another attempt in the art to provide a sanitary napkin which is longitudinally weakened is disclosed in commonly assigned Buell U.S. Pat. No. 5,171,302 issued Dec. 15, 1992 and Buell U.S. Pat. No. 5,197,959 issued Mar. 30, 1993. These references disclose a sanitary napkin having a flexure resistant deformation element which provides the sanitary napkin with a convex upward configuration when worn. This configuration is maintained due to the lateral pressure from the wearer's thighs.
Yet other attempts in the art have been made to not rely upon longitudinal embossed channels to improve fluid distribution. For example, Karami U.S. Pat. No. 4,212,302 issued Jul. 15, 1980, discloses an absorbent article having hydrocolloid material in the side margins and end margins, spaced from the fluid receiving region of the pad. The fluid receiving region is in the central portion of the pad and is substantially free of the hydrocolloid materials. However, this arrangement suffers from the difficulties associated with having both longitudinal and transverse hydrocolloid distributions necessary to provide the central region free of hydrocolloid material. Compounding this problem Karami requires an additional manufacturing step, i.e., that the surface against which the hydrocolloid materials are to be placed is first wetted. Even with this additional manufacturing step, if the Karami hydrocolloid material is near the topsheet of the absorbent article, there is a risk of the hydrocolloid material contacting the skin of the wearer.
Accordingly, it is an object of this invention to provide a sanitary napkin which does not rely upon crush resistance to maintain the target area. It is further an object of this invention to provide a sanitary napkin having differential flexibility, so that lateral hinging occurs in lieu of lateral crush resistance. It is further an object of this invention to provide a sanitary napkin which does not rely upon embossed lines for adequate fluid handling characteristics.